In recent years, mobile phones and other electronic devices have become more compact and powerful, which also accelerates size reductions of electronic parts used for the electronic devices. The miniaturization inconveniently decreases a withstand voltage of electronic devices and parts, which often causes damage to electric circuits in an electronic device due to electrostatic pulses generated when a terminal of the device makes contact with the human body. The generation of the electrostatic pulses allows high-voltage pulses—ranging from few hundreds of volts to few kilovolts with a rise time shorter than one nanosecond—to be applied to electric circuits in the device.
To address the problem of the electrostatic pulses, in conventional cases, a static-electricity control part is disposed between a line having static electricity and ground. However, recent technology achieves transmission rates of signal lines higher than few hundreds Mbps. Under the circumstances, a static-electricity control part with large capacitance causes degradation in signal quality. It is therefore preferable that the capacitance of a static-electricity control part should be kept smaller as possible. It becomes necessary to prepare a static-electricity control part with capacitance smaller than 1 pF for high transmission rates beyond few hundreds Mbps.
To address the problem of static electricity in a high-speed transmission line, a plurality of static-electricity control parts are conventionally used for protecting an integrated circuit having multiple signal terminals and ground terminals from static damage. However, using more-than-one static-electricity control parts has inconveniently increased the mounting process for integrated circuit implementation.
To decrease the mounting process for an integrated circuit, there is a growing demand that a plurality of static-electricity control parts are integrated into a single chip according to the arrangement sequence and spacing of the signal terminals and the ground terminals of an integrated circuit.
For example, patent document 1 below is known as the prior art relating to the present invention.
According to the conventional static-electricity control part described in patent document 1, as is shown in FIG. 10, common electrode 1 and a plurality of top electrodes 2 are formed, with gap 3 provided therebetween, on the top face of insulating substrate 4. Common electrode 1 is connected to the ground terminal of an integrated circuit; on the other hand, top electrodes 2 are connected to a plurality of signal terminals of the integrated circuit. The space formed between top electrodes 2 and gap 3 formed between common electrode 1 and top electrodes 2 are filled with overvoltage protection material layer 5.
Hereinafter will be described mechanism for exhibiting characteristics of the aforementioned static-electricity control part where gap 3 between top electrodes 2 and common electrode 1 is filled with overvoltage protection material layer 5.
That is, when overvoltage caused by static electricity is applied to gap 3 between top electrodes 2 and common electrode 1, “discharge current” flows between conductive particles or semiconductive particles scattered in overvoltage protection material layer 5 disposed in gap 3 between top electrodes 2 and common electrode 1. Current flows between the conductive particles or the semiconductive particles scattered in overvoltage protection material layer 5, making a detour as a scattered flow—with no concentration at a specific place—to the ground terminal.
According to the conventional static-electricity control part described in patent document 1, the space between top electrodes 2 is filled with overvoltage protection material layer 5. The structure above easily causes crosstalk between adjacent signal terminals. Besides, the conventional structure above has a small contact area of alumina-made insulating substrate 4 and a protection resin layer, by which the protection resin layer has insufficient adhesion strength, resulting in poor reliability. Further, using a high amount of overvoltage protection material layer 5 has been an obstacle to cost reduction.
patent document 1: Japanese Unexamined Patent Application Publication No. 2000-188368